1. Field of the Invention
The present invention relates to a method of making a self-inflating air mattress.
2. Description of the Prior Art
Since air mattresses are commonly used by campers who are backpacking their supplies and camping gear to a remote site, it is highly desirable that an air mattress be lightweight, compact, reliable and convenient. A quite common type of air mattress is one made up of a plurality of interconnected inflatable tubes arranged in the rectangular configuration of a mattress. Because of the inconvenience of inflating such an air mattress at the campsite, and also because of the discomfort that results from the air mattress being deflated by an accidental puncture at a remote campsite, many campers have abandoned the concept of an inflatable air mattress and have gone to a rectangular sheet of compressible plastic foam material for use as a mattress. This foam material can be rolled up into a reasonably compact package, and yet while being resilient, it has sufficient resistance to compression to provide reasonable comfort for a person lying thereon (at least by the standards of backpackers who travel to remote campsites). For the foam to have sufficient resistance to compression to provide an adequate degree of comfort, quite commonly a foam having a 25% ILD (indentation load deflection) of at least about 35 pounds is selected. Often, a more dense foam material is used to give greater resistance to compression, i.e., in the range of 2.75 pounds per cubic foot or greater. However, as higher compression resistance foams are used to give more support, the foam pad becomes more difficult to roll up and in some cases more weight is added to the backpacker's load.
With the inflatable air mattress and the foam pad each having its own particular advantages, it has been attempted in the prior art to combine both constructions into one article. One such mattress is shown in the Swiss Pat. No. 428,124, this mattress comprising an outer rectangular shaped air impervious envelope and an interior foam core. The patent notes that the air mattress can be compressed into a stowed position (i.e., rolled up to a relatively small volume), after which the inflating valve of the air mattress is closed to maintain the mattress in its compact stowed configuration. When the valve is opened, the force of the foam core causes the mattress to self-inflate to its expanded position, after which the valve is closed to contain the entrapped air. The patent also notes that the foam core, in addition to providing the self-inflating characteristic of the mattress, also functions as a foam pad to provide support as "emergency upholstery" in the event that the outer covering develops a leak. Thus, the essential construction of the air mattress of this Swiss patent is an interior foam pad having sufficient resistance to compression to provide some reasonable degree of support to a person lying thereon, enclosed by an airtight envelope that functions as an inflatable air mattress.
A somewhat related concept is disclosed in U.S. Pat. No. 2,997,100, where there is shown a foam filled mattress of a design more commonly used for a conventional household bed. The envelope of this mattress is airtight and can be inflated to a desired pressure, with the air pressure providing a certain degree of additional support for a heavier person. The patent notes that this solves the problem of being able to provide resonable consistency of firmness of the mattress for persons of greatly differing weights. Thus, the overall structure of this mattress utilizes the supporting force provided by the compression resistance of the foam core, with the foam core having sufficient pressure resisting quality to provide a resonable degree of support in compression loading.
A more recent approach to providing a self-inflating, foam filled air mattress is disclosed in U.S. Pat. No. 3,798,686. In this patent the resistance of the foam core to compression is utilized in the same manner as the mattress of the abovementioned Swiss patent to give the air mattress its self-inflating characteristic. However, instead of utilizing the compression resistance of such foam to any great degree to provide support to a person lying on the mattress, this particular mattress depends upon the foam core, in the configuration of a matrix of foam ribs, to provide a tie between the upper and lower skins of the mattress to prevent ballooning of the mattress. The foam core shown in this patent comprises upper and lower continuous sheets of foam, between which are two layers of crossing foam ribs arranged in a lattice. These foam components are all bonded one to another, and the upper and lower layers of foam are bonded to the air impermeable upper and lower skins of the air mattress envelope. Also, the patent specifies the use of a lightweight foam material for the core, having a density in the range of about 0.8 to 1.5 pounds per cubic foot, with an advantageous material being polyether foam of a density of about 1.1 pounds per cubic foot.
By way of further background information, other examples of foam filled structures are disclosed in the following patents: British Pat. No. 984,604; U.S. Pat. No. 1,159,166, Brawner; U.S. Pat. No. 2,834,970, Nappe; U.S. Pat. No. 3,323,151, Lerman; U.S. Pat. No. 3,378,864, Cornes; U.S. Pat. No. 3,537,116, Kain; and U.S. Pat. No. 3,611,455, Gottfried.
While the prior art has recognized the value of using both an inflatable envelope and a foam core in combination, and while the prior art has further recognized the function of the foam acting in compression to provide support, and also as a local tie between upper and lower surfaces of the mattress to prevent ballooning, and has recognized the function of the foam to give the mattress its self-inflating feature, the prior art has failed to recognize how a foam core can be utilized in combination with an air impermeable envelope in a manner to utilize properly the structural and load bearing characteristics of these components to get full value from these components to optimize such qualities as compactness, durability, convenient stowing, and proper utilization of the components of the mattress to provide proper support characteristics of the mattress.
It is an object of the present invention to provide a process for the manufacture of a foam filled air mattress having an optimized configuration with regard to the features noted above.
With regard to prior art relating to the method of the present invention, the following patents are generally related to the making of plastic articles and the like by application of heat and pressure applied either by a vacuum or application of positive pressure. These patents are: U.S. Pat. No. 1,908,682, Bronson; U.S. Pat. No. 2,698,273, Miner et al; U.S. Pat. No. 3,462,330, Greig et al; U.S. Pat. No. 3,654,012, Schlager; U.S. Pat. No. 3,668,032, Bunting et al; and U.S. Pat. No. 3,818,823, Bond.
The following patents are generally related to plastic and/or foam structures of various types. These patents are: U.S. Pat. No. 3,619,344, Wolinski; U.S. Pat. No. 3,779,847, Turner; U.S. Pat. No. 3,817,803, Hirsky; U.S. Pat. No. 3,818,962, Muller-Scherak, and U.S. Pat. No. 3,829,918, Stamberger.